Question: Luis is 75 years old and Daniel is 15 years old. How many years will it take until Luis is only 4 times as old as Daniel?
Explanation: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Luis will be $75 + y$ years old and Daniel will be $15 + y$ years old. At that time, Luis will be 4 times as old as Daniel. Writing this information as an equation, we get: $75 + y = 4 (15 + y)$ Simplifying the right side of this equation, we get: $75 + y = 60 + 4 y$ Solving for $y$ , we get: $3 y = 15$ $y = 5$.